The aluminum industry techniques have been known for more than a century in all the aluminum plants all over the world such as, for example, the Hall-Heroult process. Such premises usually incorporate attached thereto what we know as anode plants which are essential elements in this kind of industry.
The process for manufacturing anodes presently in use comprises the production of a mixture of petroleum coke with residual reduction anodes known as butts, and electrolytic pitch which is obtained from the tar. The first two ingredients, that is, petroleum coke and residual reduction anodes are submitted to crushing, sieving and classifying operations in specific granulometric fractions in such a way that after they are mixed, they may produce the highest "packing" degree that can be attained for the purpose of using as little binding agent and obtaining the best mechanical properties for the anode.
All the above mentioned fractions are heated and subsequently mixed to the electrolytic pitch. This operation is carried out in continuous or batch mixers by using temperature range from 80.degree. C. to 350.degree. C. depending on the process used.
The result of the mixing step described above is a slurry which may be directly used in the electrolytic reduction vats when the aluminum is produced through Soderberg process, for producing the required anode for the reduction process. Said anode is produced by baking said slurry in the heat of the reduction vats which operate at temperature from 900.degree. C. to 1,000.degree. C.
Alternatively, said slurry may also be pressed or compacted or vibrocompacted in suitable presses or compactors, with or without vacuum, in order to produce green anodes which are usually designed to be used in the process known as pre-baked process.
However, before being used in the pre-baked reduction process, said green anodes should be submitted to baking in special furnaces which may be open or closed. In such furnaces, the green anodes are baked within a temperature range from 900.degree. C. to 1,200.degree. C. in order to attain the required physical and chemical properties to be used in furnaces for reducing alumna to primary aluminum.
It is also known by those skilled in the art that during the process for the preparation of the above-mentioned anodic slurry for the Soderberg process, as well as during the process for baking the green anodes for the pre-baked process, aromatic components are released from the electrolytic pitch and despite the fact that they are below the limits set out by the regulations of a number of countries they are deleterious either by inhalation or contact and the result is a noxious environment.
Another typical inconvenience from the use of electrolytic pitch is that since it is in the solid form dust is generated and often the plant operators get burned by exposing the skin in contact with the dust under the sun. Said burns are deemed as quite severe.
Another inconvenience in the use of solid electrolytic pitch is related to the dirty caused in the plant area and the frequent problems at navigation ports when handling the electrolytic pitch which is usually transported by ships.
Trying to minimize the above-mentioned inconveniences, systems based on the gas treatment in association or not with efficient dust removing systems have been used. Also to minimize said inconveniences it has been tried to replace solid electrolytic pitch by liquid electrolytic pitch. However, such resources are not fully efficient and demand very high investment costs.